Sealant having epoxide encapsulated by aminoplast shell and polymeric binder

ABSTRACT

MECHANICAL FASTENERS AND STABLE PRESSURE-ACTIVATABLE ADHESIVE SYSTEM THEREFORE BASED ON ENCAPSULATED RESIN, PREFERABLY EPOXY AND NON-VOLATILE CURATIVE THEREFOR, PREFERABLY AN AMINE SUCH AS 1,3-BIS-4-PIPERIDYLPROPANE OR IMIDAZOLE, THE CAPSULES AND CURATIVE BEING CONTAINED IN POLAR SOLVENT-FREE BINDER WHICH CAN HOLD SYSTEM ON A BUTMENT SURFACES OF FASTENER.

Feb. 15, 1972 w -r ETAL 3,642,937

SEALANT HAVING EPOXIDE ENCAPSULATED BY AMINOPLAST SHELL AND POLYMERICBINDER Filed Dec. 22, 1969 INV NTORS ALE/W 750M QEDH/flEC/(EPT WORA/EYSUnited States Patent Office 3,642,937. Patented Feb. 15, 1972 U.S. Cl.260-834 12 Claims ABSTRACT OF THE DISCLOSURE Mechanical fasteners andstable pressure-activatable adhesive system therefore based onencapsulated resin, preferably epoxy and non-volatile curative therefor,preferably an amine such as 1,3-bis-4-piperidylpropane or imidazole, thecapsules and curative being contained in polar solvent-free binder whichcan hold system on abutment surfaces of fastener.

This invention relates to improved self-locking fastening devices,particularly employing threaded mechanical fasteners such as bolts,screws, nuts, pipe joints, threaded nails, and the like, and to novelstable latent curing adhesive cements suitable for use in conjunctiontherewith. This application is a continuation-in-part of copendingapplication Ser. No. 638,428, filed May 15, 1967 now abandoned.

Various fastening devices have been proposed or used utilizing adhesivesor plastics in one way or anothenm attempting to prevent the fastenersfrom loosening during use or service. Ideally, such a fastener-lockingsystem should be capable of easy manufacture or assemblage by thefastener manufacturer. It should be tackfree and nonblocking so thatmany fasteners can be shipped and stored in barrels or other containerswithout adhering to each other or being tacky to the touch, so as to bedifficult to handle or gather dust. The adhesive applied to the fastenershould have long term stability both before and after application sothat both the adhesive and the coated fasteners may be handled andstored in accordance wlth conventional procedures without degrading theadhesive. In use, the fastening device should be capable of beingreadily applied without undue increase in the amount of work or inputtorque necessary to install the fastener. The adhesive should curerapidly so that the fastener may be used after only a short cure periodand provide a bond, such that substantially increased work or back-offtorque is required to remove the fastener. Desirably, also, such asystem should be capable of reuse after removal of the fastener, and theadhesive should provide some latent curing which would enable a fastenerwhich has slightly loosened, due to vibration or other stresses, to.become refastened rather than dropping out of place.

Insofar as we are aware, however, no one prior to the present inventionhas provided any commercial practical self-locking fastener having thesefeatures. Fastener systems which have been available suffer from one ormore drawbacks.

One fastener sealing adhesive system in present commercial use involvesan anaerobically curable adhesive which is applied to the fastener inliquid form immediately before the fastener is to be installed. Theadhesive cures after installation of the fastener due to the absence ofoxygen between the abutment surfaces of the fastener and other surfaceswhich they contact. Such systems suffer from the disadvantage that theymust be applied by the ultimate user of the fasteners, rather than bythe fastener manufacturer. Moreover, once the cure is completed, it isno longer possible for refastening to occur if the fastener is slightlyloosened in service.

Another commercially used fastening means involves the application of aslug of deformable material, such as a nylon plastic, in a cavity on thefastener surface; for example, in the threaded area. Such devices doprovide an increased prevailing torque if the fastener is slightlyloosened, but in addition to being costly, suffer from the disadvantagethat more work is normally required to install the fastener than toremove it.

A further system is that disclosed in U.S. Pat. 3,061,455 (Anthony)granted Oct. 30, 1962, wherein two separated strips of co-reactants areapplied to the threads of a bolt. This system requires two separateapplications of the adhesive materials, and generally a furtherapplication of a protective polymer coating. The bolts cannot easily beshipped in contact with others because of the likelihood of contact andpremature reaction of the coreactants due to contact of resin on onebolt with curing agent on another.

Another system which has been proposed is that described in Schultz etal. US. Pat. 3,179,143, granted Apr. 20, 1965, which system is a latentcuring singlecomponent adhesive coated on the abutment surfaces ofthreaded fastening devices. Co-reactants which together form theadhesive are separated from each other by encapsulation inmicroscopically small capsules which rupture upon the application ofpressure to mix the coreactants thus activating the adhesive. Prior tothe present invention, systems of the type disclosed in the Schultz etal. patent have sulfered from a lack of stability not hitherto fullyunderstood. Apparently the commercially used capsules, formed fromaminoplast polymers, are not entirely impervious especially after longterm storage in contact with many amine epoxy curatives. These amines,especially in the presence of moisture, appear to swell or otherwiseattack the capsule walls, causing premature cure of the adhesive withresultant loss of adhesive locking strength.

A number of interrelated shortcomings impair the performance of previousformulations especially after extended shelf storage. Amines such asaminoethyl piper- .azine disclosed in the Schultz et al. patent, whichare capable of curing epoxy resins at room temperature apparentlyvolatilize and escape from the adhesive over too short a storage periodto be commercially acceptable. Other less volatile amines, such asdicyandiamide either will not cure the resin at room temperature or areimmiscible with the resin when released from the capsules; thus theadhesive does not cure rapidly, if at all, at room temperature. The morevolatile amines apparently vaporize and escape, even when covered by acoating of a material such as methyl cellulose.

The water-based, hygroscopic methyl cellulose binder apparently initself causes instability due to its tendency to pick up moisture fromthe surroundings. Instability due to water is unexpected since thecapsules are manufactured in an aqueous slurry and are found stable inthe presence of moisture in other applications. Unknown forces, perhapsthe Water in combination with an amine curative, apparently cause theinstability which is overcome in accordance with the present invention.

The present invention provides a significant advance over the structuresdescribed in the Schultz et al. patent and other prior art in that itprovides novel self-locking fasteners (and the latent curable adhesivesfor use therein) which permit the use of known capsules for containingan adhesive co-react-ant, which yet have the commercially requiredstability and capability of withstanding prolonged storage and handling.Insofar as we are aware, this invention provides the first self-lockingfasteners, coated with an adhesive system, capable of being stored formany months in drums, barrels or crates, shipped in commerce, and thenused by simply turning a mating element such as a nut into place toform. a bond which requires significantly greater 'force to loosen thebond than is required to tighten the fastener into place. The bondsformed are sutficient to withstand substantial vibration encountered inindustrial machinery, automobiles, or refrigerators.

The adhesive system, prior to application to the fastener can be shippedin commerce and stored for weeks or months without premature cure andcan then be applied to fasteners and then further stored for extendedperiods at ambient temperatures (which normally fluctuate wide y), andcured at room temperatures upon physical rupture of the microcapsules.If desired, cure can also be accelerated by the application of heat tothe composition, but room temperature cures are ordinarily preferred forconvenience of application. The adhesives of this invention can beapplied to fasteners in one single coating process and can be applied toany abutment surfaces of the fastener, to which sufficient pressure isapplied to cause rupture of the capsules on application of the fastener.The threads of a threaded mechanical fastener are preferred because bothcompressive and shearing forces can be applied to the adhesive to insurerupture of the capsules and mixing of the co-reactants.

In accordance with the present invention, it has been discovered thatcertain preferred combinations of curing agents and binders can beutilized together with aminoplast polymer capsules to provide stableostensibly one part adhesives which are not only non-tacky, but whichare also stable in humid atmospheres. These adhesives contain a curingagent which is readily miscible with the resin used, and which willrapidly cure the resin at ordinary room temperatures. Adhesives of thisinvention may be applied to fasteners and stored for at least twelvemonths, and generally much longer, under normal conditions without anysignificant loss of adhesive properties. The adhesives of this inventioncan be applied to the abutment surfaces of a fastener, or to othersurfaces to be joined to which sufi'lcient pressure or shear forces canbe applied to effect rupture of the capsules. The adhesive is activatedat room temperatures by application of pressure and/or shearing forcesthereto, for example, upon tightening of the fastener. Otherapplications include plates or articles which are joined together undergreat pressure, preferably with simultaneous application of frictionalshearing forces, to the surfaces being bonded. The improved adhesivesystems of this invention are substantially free of water and otherpolar solvents and contain essentially non-hygroscopic ingredientsincluding an encapsulated resin, a substantially non-volatile curingagent which is miscible with said resin, and an organic polymeric binderfor said resin and curing agent. Since the adhesive systems of thisinvention are substantially waterfree (desirably containing less thanone percent water by weight of adhesive composition), fasteners coatedtherewith have less tendency to corrode than do those coated withwater-based systems.

The improved self-locking fasteners of this invention are formed byapplying the improved adhesives to the abutment surfaces thereofespecially to the threaded portion of a threaded mechanical fastenersuch as the threads of a nut or bolt. Such fasteners are generallyformed from a rigid structural material such as metal, wood, glass,ceramic, or a plastic such as nylon or polyvinyl chloride, and mayinclude bolts, screws, nuts, pipe fittings, etc. Other mechanicalfasteners to which the improved adhesives may be applied include dowels,nails, rivets and staples, in which case the adhesive is applied to theshank and/ or under the head, etc. of the fastener. The adhesiveformulations can be applied to the fasteners by dipping, spraying, stripapplication of molten material extruded on the fastener, rollapplication, or other techniques which will be apparent to those skilledin the art.

The invention will be further illustrated by the accompanying drawing,wherein FIG. 1 is an enlarged crosssectional view of a fastenerillustrating one embodiment of the invention.

Bolt 10 is coated, preferably on threads 12, with adhesive 14. Adhesive14 preferably consists of a matrix portion which is a polymeric binder18 having distributed therein capsules 20 (shown greatly enlarged) whichcontain a curable resin. A curing agent for the resin is alsodistributed throughout the binder matrix. As nut 22, or equivalentmating threaded device, is run onto bolt 10, some of capsules 20 areruptured by the shearing forces produced. The shearing forces caused byrunning nut 22 onto bolt 10 also effect thorough mixing of the resinreleased from the capsules with the curing agent, thus promoting rapidthorough cure of the released resin. Capsules not ruptured by the firstuse of the fastener can be ruptured, for example, due to vibration.Thus, the fasteners of this invention are both re-useable, and capableof refastening themselves if slightly loosened in use.

The preferred resins are liquid 1,2-epoxy resins, contained withinmicroscopically small capsules which range in size from 5 to 500microns, and preferably 25 to 150 microns. Examples of the preferredepoxy resins include 1,2-epoxy reaction products of polyhydric phenolssuch as bisphenol-A and epichlorohydrin or polyglycidyl ether,epichlorohydrin with phenolformaldehyde condensation polymers andepichlorohydrin with amine phenols.

The preferred polyepoxides contain an average of more than 1 andgenerally more than an average of about 1.5 oxirane groups per molecule.Examples of the preferred resins are liquid polyglycidyl ethers ofbisphenol-A which have slightly less than two oxirane groups per averagemolecular weight (for example, Epon 815, or ERL-2795). Examples ofresins having more than two oxirane groups per average molecular weightare polyglycidyl ethers of phenol-formaldehyde novolaks (for example,D.E.N. 438, which has a functionality of 3.6, or the trifunctionalnovolak Epiphen BR. 823). When highly viscous resins such as the latter,or even solid resins are used, for example, in order to provide somedesired property such as temperature resistance, etc., it is preferredto form a blend with a less viscous resin such as ERL-2795. Furthersuitable resins include polyglycidyl ethers obtained from the reactionof dihydric or polyhydric alcohols with epichlorohydrin, for example,resins made by condensing epichlorohydrin and glycerin to give diandtri-epoxides having a functionality of about 2.2 (e.g., Epon 182) andpolyglycol polyepoxides such as the diglycidyl ether of polypropyleneoxide (e.g., D.E.R. 736). Further examples will be apparent to thoseskilled in the art.

For the preferred epoxy resin systems, it has been found that there areseveral important characteristics for the curing agent used. Firstly, inorder to be useful, the curing agent should cure the resin to a toughinfusible state within about 24 hours at room temperature. Preferredcuratives, however, produce a significant amount of cure within ashorter time, within a few minutes up to about 6 hours. Also, it isimportant that the curative be substantially nonvolatile and capable ofbeing stored at exposed to the atmosphere for at least about one weekwithout losing more than 2% of its Weight. Curatives having thischaracteristic have been found to be useful in forming adhesives havinglong term storage stability on bolts or other fasteners at ambienttemperatures. Preferably the curative should not lose more than 2%weight when a 2.0 gram sample is heated in an open vessel in anoncirculating oven heated to 136 F. (temperature fluctuation beingcontrolled to within :2 degrees) for 12 days.

A third and very important characteristic is that the amine must have atleast about 50 or more atomic weight units per amine group. Amineshaving a higher functionality than this (i.e., less than about 50molecular weight units per amine group), while often being good roomtemperature curatives, have been found to produce instability,apparently by attacking the walls of capsules formed from condensationpolymers such as urea-formaldehyde.

The substantially non-volatile curing agent may :be in either solid orliquid form so long as it is miscible with the resin used, i.e. willrapidly dissolve when mixed with the resin. The miscibility of the aminein the resin can be determined by means of a simple spatula test byplacing resin in a container and mixing in a chemically equivalentamount of the amine while stirring slightly with a spatula. Amines whichare sufficiently miscible in the resin will convert the resin to a hardinfusible solid Within about eighteen hours. Other useful amines willdissolve in significant amounts and cause an increase in viscositywithin this time period, but may require as much as 7 days to reach ahard resin stage. The latter curatives can be used in cases where thelonger cure times are not a problem. If the amine is not sufiicientlymiscible with the resin, cure will not occur and two discontinuousphases may be present in the container.

Examples of suitable substantially non-volatile amine curing agents forpolyepoxide resins are: imidazole, 1,3- bis-4-piperidy1 propane,1.6-hexane diamine, 4,4'-methylenedianiline, substituted alkylenediamines and liquid polyamide resins such as Versamid 125 (a dimerizedunsaturated fatty acid reacted with alkylene diamines). It will beunderstood that curing agents which are in themselves volatile cansometimes be converted by chemical reaction to a substantiallynon-volatile form. For example, liquid amines can be reacted with acidsto form solid amine salts having reduced vapor pressure. For example,the tetraethylene pentamine can be reacted with a fatty acid to give asalt useful as a curing agent.

The preferred amine curing agents for polyepoxide resins are stronglybasic amines which in saturated solution in water will have a pH valueof at least about 9.5. Amines more weakly basic than this tend toprovide a cure rate for the adhesive less than the optimum. The curingagent in generally added in approximately a stoichiometric amount.However, those skilled in the art will recognize that lesser amounts canbe used in the case of curatives which have a catalytic curing effect onthe resin.

The binder resin used to bind together the capsules and curing agentshould be an organophilic, hydrophobic water insoluble organic polymericmaterial capable of being stably dispersed in solvents which have asolubility parameter of less than 9 (as discussed below) and a hydrogenbonding strength of poor to medium (i.e. which are free or substantiallyfree of highly polar functional groups such as hydroxy, amino, amido,and carboxylic groups), the binder material further being capable offorming a self-sustaining film when cast from said solvents. Adhesivesof the invention which contain these binder resins will, on cur-ing ordrying of any solvent therefrom, result in a solid non-tacky coating atroom temperature on the fastener to which the adhesive composition isapplied. Preferred binder resins of this invention are organophilichydrophobic water insoluble polymers which are soluble to at least about6 weight percent in toluene at 70 F.

The binder is added to the adhesive composition in amounts sufficient tobind the other ingredients in the adhesive together without crumbling orpeeling away from the fastener surface. Generally somewhat largeramounts of binder resin are necessary in the case of liquid curingagents in order to provide a formulation which will dry to a solidsubstantially tack-free state. Examples of suitable binder materialsinclude butadienestyrene copolymers, either of the GRS or stereospecificblock copolymer type, butadiene-acrylonitrile copolymers, polyvinylbutyral polymers, butyl rubbers, solid polyamid resins, toluene-solublepolyurethane resins, polychloroprene polymers, soluble copolymers ofethylene and propylene, polystyrenes, soluble polyvinyl chloridepolymers and copolymers, low acid number hydrocarbon resins, such asasphalt, and blends of such materials.

In one preferred embodiment of the invention, the binder resin isdissolved in a solvent therefor and the capsules and curing agent aremixed therein. This mixture can then be applied to bolts or otherfasteners by dipping, brushing, spraying, etc., and the mixture dries toa tack-free film upon evaporation of the solvent. The solvents usedshould have low polarity, aromatic solvents such as toluene and benzene,which are free of hydroxyl and amino functional groups, being preferred.Polar solvents, particularly water and alcohols, should be avoided inorder to avoid damage to the capsule shells and/or premature reactionwith the curative. Useful solvents have been found to have a solubilityparameter of about 9 or less, and a hydrogen bonding capability of frommedium to poor. Numerous solvents are listed and discussed according tosolubility parameters and hydrogen bonding capability, in PolymerHandbook, Interscience Publisher, 1966, at pages 341-358.

In another embodiment of the invention, the binding resin is in the formof a relatively low temperature melting material. The adhesivecomposition is formed by melting the resin and mixing in the capsulesand curing agent. The adhesive-containing mixture is then handled in asolid form, commonly referred to as a hot melt. This hot meltformulation is applied to the fastener by melting and applying to theabutment surfaces of the fastener, or may simply be applied by rubbingthe formulation over a fastener, particularly the threaded portionthereof. The hot melt type formulations provide cost and safetyadvantages in that the use of the volatile solvent, which is usuallylost on volatilization, and which may cause odor and fire hazards, iseliminated.

In a still further embodiment of the invention, the adhesive can beformed into a flexible film. Such films can be formed by using apolymeric binder which is a rubbery film-forming material containing thecapsules and curing agent, and casting the same onto a flat surface inthe form of either a molten or solvent-containing liquid, and hardeningeither by cooling or evaporating the solvent. Films thus formed can bestamped into washers which can then be applied to fasteners in the usualmanner, or the film may be used as a thread wrapping means. In thelatter applications, the film is simply wrapped around the threadsbefore application of the mating threaded part, which causes rupture ofthe capsules due to the combined pressures and shearing forces. Suchfilms can be wound and supplied in the form of a tape.

Whatever the form the adhesive takes, in the interest of maximum storagelife, it should be essentially waterfree, preferably containing no morethan about one percent by weight of total adhesive composition. Ifnecessary, all the ingredients can be dried, e.g. by moderate heating orusing drying agents, prior to formulation of the adhesive.

The invention will be further illustrated by means of the accompanyingexamples in which all parts are given by weight unless otherwiseindicated.

EXAMPLE I A urea-formaldehyde resin pre-polymer solution was prepared byreacting an agitated mixture of 38.8 lb. (17.6 kg.) 37% Formalin, 0.188(85.2 gm.) triethanolamme, 14.5 1b. (6.56 kg.) urea for two hours at 70C. (158 F.). After this reaction period the resulting solution wasdiluted with 178 lb. (80.8 kg.) cold water.

The encapsulation of ERL 2795 epoxy resm, a bisphenolepichlorohydrinreaction product was carried out in a 50 gallon reactor having thedimensions of 34 h. x 22 /2 d. with 4 baffies 2" wide fitted with a 4"flat blade turbine agitator 8" from the tank bottom as follows: Thepre-polymer solution above was adjusted to a pH of 7.0 with 160 ml. 3 Nhydrochloric acid at 222 C. (72 F.) after which was added 60 lb. (27.2kg.) ERL-2795. The agitation speed was adjusted to 1230 r.p.m. andagitation continued for 34 minutes to insure equilibrium mixing prior toinitiating the encapsulaton reaction. The acid catalyzed polymerizationreaction leading to formation of deposited shell walls ofurea-formaldehyde resin was catalyzed by adding 448 ml. 3 N hydrochloricacid at a rate of 40 ml. per minute to a pH value of 2.2. The reactionwas maintained at 233 C. (74 F.) for one hour after the pH was reducedto 2.2 at which time the temperature was increased to 40 C. (104 F.).The encapsulated epoxy resin product was recovered after overnightreaction by neutralizing (pH=7) with 27.5% sodium hydroxide, filtrationand water washing of the slurry and drying in a forced air oven at 120F. The capsule size range was 2575,u.

8.0 gm. of polyvinyl butyral resin were dissolved in 92 gm. of toluenewhich had been heated to 140 to 150 F. 32 gm. of l,3-bis-4-piperidylpropane, an amine having 105 atomic weight units per amine group, wasadded to this hot solution, and the resulting mixture was agitated fortwo hours until the amine had completely dissolved. The mixture was thencooled to room temperature (75 F.) and 80 gm. of the capsules(containing about 60 gm. of epoxy resin) were then added, and theresulting mixture agitated until the capsules were well distributedthrough the solution. After standing for approximately 48 hours, thecapsules had settled to the bottom of the container, but could beredistributed by agitation.

The adhesive was tested by dipping a /z" diameter, 13 threads to theinch, 1 long, hex head cap screw, into the adhesive, threads first,lifting the bolt out, and allowing the adhesive to dry on the threads.The amount of dry adhesive was usually from .3 to .45 gm. After 24 hoursat room temperature, and 2 hours at 160 F., the toluene solvent hadevaporated, leaving a non-tacky film of the adhesive on the threads ofthe bolts. The adhesive was tested by mating an appropriate sized nut tothe bolt and running the bolt into the nut with 30 ft. lbs. (416kg.-cm.) of run in torque. After 24 hours, the breakloose torque wasmeasured, with a torque wrench, and if prevailing torque was measured,the same measurement was made by recording the amount of torque requiredto move the bolt out of the nut after /2 and 1 full revolution frombreak-loose. Typical values were 5-0, 48 ft. lbs. (692, 664 kg.-cm.) forbreakloose torque and 2832 (388-444 kg.-cm.) for prevailing torque.Values for nuts and bolts without adhesive were 21 ft. lbs. (291kg.-cm.) for break-loose torque and for prevailing torque. The treatedbolts of the present example demonstrated a similar increase inbreak-loose torque after being stored for 52 weeks before being used.The adhesive bond after being formed also remains essentially stableafter more than one year.

Tests were also conducted with /8 x 1% inch Grade cap screws withmatching nuts. All metal parts were degreased with acetone and driedbefore adhesive application. The bolts were dipped into the adhesive sothat sutficient threads were covered to engage the nut with two threadsexposed on the backside of the nut.

On these /3 inch screws, the adhesive covered about .85 inch of thethreads. Excess adhesive was permitted to drain from the screws forabout 10 seconds, then any additional excess material was scraped ontothe edge of the can containing the liquid adhesive. Solvent removal waseffected by letting the screws stand upright on the head for 24 hours atroom temperature, then for 2 hours at 160 F. in an oven. After thistreatment, about .18 to .20 gram of adhesive containing approximately 1%solvent was left on the threads of the screw. This constitutedsufiicient excess so that adhesive was extruded from the mating surfaceswhen the screw was tested.

Ability of the adhesive to provide bonds after re-use was tested onthese bolts using a procedure simulating actual use. A hardened steelwasher was placed between the head of the bolt and a mild steel platewhich had a hole drilled for insertion of the bolt. A second hardenedsteel washed was placed under the nut on the exposed side of the boltand the nut was tightened to 31 ft. lbs. seating torque with at leasttwo threads exposed outside of the nut. A 24 hour cure time at roomtemperature was used before the break-loose torques were measured. Thebolts were reseated immediately after making the complete measurementfor each cycle. Results are shown in Table I. The break-loose torque ofthis assembly without adhesive was 25 ft. lbs. Each of the figures givenis the average of 8 test samples. Similar assemblies were also tested byexposure to gasoline, oil, and water immersion, outdoor exposure, andsalt spray, for one month. The adhesive in each case withstood theexposure without significant loss of adhesive properties.

TABLE I (PIT) pre- (ST) (BLT) (POT) prevailing in seating breakloosevaillng out torque, ft. torque, it. torque, it. torque, It. Reuse lbs.(kg-cm.) lbs. (kg.cm.) lbs. (kg-em.) lbs. (kg-cm.)

Initial. 0.5 (7) 31 (420) (553) 9 (124) 6.5 (00) 31 (420) 32 (443) 6(83) 2.8 (37) 31 (420) 27 (373) 3 (41) 1.5 (21) 31 (4'29) 25 (346) 2(28) 1.0 (14) 31 (420) 23 (318) 4 (6) l Prevailing in torque increasesas the nut is screwed on until all 01' the treads are engaged. Thisvalue is then a maximum until the screw is seated and is the reportedvalue.

Seating torque commercially recommended for (zrade 5, inch screws togive a fastener tension between and of the ultimate yield strength ofthe fastener material.

3 Prevailing out torque was an average value taken at the end of thefirst revolution out during steady, even removal 01 the bolt.

It has also been found that the stability of the adhesive for long termstorage can be improved by drying the capsules at elevated temperaturesof 200 to 350 F. It has also been found preferable to use H SO in placeof I-ICl and Na SO in place of NaCl in the capsule making procedure.Melamine can also be substituted for about 8% (on an equivalent weightbasis) of the urea in order to bring about a further improvement in thecapsule stability. These improved capsules, which are the subject ofanother patent application, enable the use of a wider variety ofcuratives than possible with capsules previously known. The capsules canalso be treated with a solution of an alcohol such as furforyl alcoholimmediately before drying. This latter treatment apparently has theeffect of chemically tying up any amine-reactive chemical groups in thecapsule shell walls, and makes the capsules more readily dispersible inorganic solvents and binders.

EXAMPLE I-A To the adhesive mixture of Example I was added 8.4 grams ofa micron-size synthetic silica filler (Syloid 244), with sufiicientagitation to provide a uniform mixture. The advantages derived from suchfiller are twofold. First, after prolonged standing, e.g. for severalmonths to a year, only slight agitation is required to redistribute thesettled ingredients into a uniform system, while the mixture of ExampleI after storage may require considerable agitation to effectredistribution. Second, the strength of the adhesive is improved atelevated temperatures. T hns, break-loose torque tests were conducted in/3 x 4% inch Grade 5 cap screws with matching nuts as described inExample I. Fully cured assemblies were heated to 250 F. and tested forbreak-loose torque at this temperature. An average value of 28 ft. lbs.(388 kg.-cm.) was obtained with the filled adhesive of this examplecompared to an average value of 18 ft. lbs. (250 kg.-cm.)

obtained with the composition of Example I under the same conditions oftesting. Other performance values are similar to those obtained andlisted in Example 1. Useful results are achieved when the filler ispresent in the amount of about 2-20 grams (on the basis of Example Iamounts), with about 6-12 grams constituting a preferred range.

EXAMPLE II A mixture of 15.0 gm. of Versamid B-710, a polyamide resinmade from a long chain aliphatic dibasic acid and a polyamine having asoftening temperature of about 150" F. and an amine number of less than100, with 20.0 gm. of 1,3-bis-4-piperidyl propane, was heated to 200 F,at which temperature the mixture was a viscous solution. 40 gm. of thecapsules of Example I were stirred into the mixture to give a viscouspaste, with a viscosity at 200 of about 120,000 centipoise. This pastedid not change in viscosity at this temperature for 48 hours. This hotpaste was applied to the threads of a clean, dry bolt, along one side ofthe threads as a stripe, approximately A inch wide. The Versamid B-710served as a binder for the reactive ingredients. A nut was threaded ontothis bolt, and torqued in with 30 ft. lbs. (416 kg.-cm.) of appliedpressure and allowed to stand 24 hours before measuring the break-loosetorque. Break-loose torques of 52 (720 kg.-cm.), 54 (748 kg.-cm.), 52(720 kg.-cm.), and 57 (790 kg.-cm.) were measured for four bolts coatedand treated in the described fashion. The paste when cooled to roomtemperature hardened into a somewhat waxy solid which could be appliedto fasteners by rubbing on at room temperature or remelted and applied.

EXAMPLE III A solution A was made by dissolving 25 parts by weight of abutadiene-styrene block stereospecific copolymer in 75 parts by weighttoluene. A second solution -B was made by dissolving 50 parts by weightof Staybelite Ester No. 10, a hydrogenated wood resin, in 50 parts byweight toluene. A third solution C was made by dissolving 5 parts byweight Hycar 1072 (a butadiene-acrylonitrile copolymer containing somefree carboxyl groups) in 95 parts by weight toluene. Solution A parts)was blended with B (2.5 parts) and C (50 parts). After the mixture wasthoroughly blended, 5.13 parts of 1,3-bis-4-piperidyl 1 0 EXAMPLE IV Amixture of 16.0 grams of imidazole, 40 grams of the capsules of ExampleI, and grams of 8% polyvinyl butyral in toluene was prepared. Thismixture was thoroughly blended and then applied to the threads ofonehalf inch 13, 1" long hexagonal head cap screws, after a 24 hourdrying period at room temperature the solvent content was reduced to30%. The bolts were than fitted with nuts which were tightened to 30 ft.lbs. (416 kg.-cm.) of applied torque. After 2 /2 days cure at roomtemperature, the break-loose torque was measured and found to be 51 (707kg.-cm.), 55 (762 kg.-cm.), 58 (804 kg.-cm.), and 58 (804 kg.-cm.) ft.lbs. The average prevailing torque to maintain the removal of the nutwas 15 (208 kg.-cm.) to 20 (267 kg.-cm.) ft. lbs. Imidazole has 66atomic weight units per amine group.

EXAMPDE V An adhesive formulation was prepared by mixing 16.0 grams of4,4'-methylenedianiline, 40.0 grams of the capsules of Example I, and50.0 grams of 8% polyvinyl butyral in toluene. This mixture (after beingthoroughly blended) was also applied to the threads of /2 inch capscrews as in Example IV. The break-loose torque was measured at the endof a 2 /2 day room temperature cure. The break-loose torques weremeasured and found to be 54 (749 kg.-cm.), 60 (831 kg.-cm.), 52 (721kg.-cm.), and 58 (804 kg-cm.) ft. lbs. Average prevailing torque was 30(416 kg.-cm.) ft. lbs. on this first removal of the nut.

EXAMPLE VI Example I was repeated, substituting different binders forthe polyvinyl butyral resin. The proportions of ingredients used arelisted in Table II as are the values obtained by applying the adhesiveunder the head of a /2 bolt of the type as described in Example I,putting the adhesive in place, and allowing the adhesive to cure.

Some of the bolts with the adhesive thereon were aged at 120 F. Thesebolts were then turned into place and allowed to cure. The foot poundsof torque required to remove the latter bolts are also recorded in TableII. The numbers given in parentheses indicate the time in weeks in whichthe bolts were aged at 120 F.

TABLE II Break-loose Torque, ft. lbs. (kg-cm.) 1,3bis4- Sample PartsCapsules, pipen'dyl Aged ad- Number Binder binder parts propane Initialhesive l A 25% butadiene styrene block copoly- 10.6 64 24.4 35 (485) 27(374) mer in toluene. B 25% low molecular weight butadiene 10.6 65 24.638 (374) 27 (374) styrene block copolymer in toluene.

1 Aged 3 weeks.

propane was dissolved in the mixture and 11.25 parts of EXAMPLE VIIcapsules fill, 10 to 120p diameter) were stirred in until the resultingmaterial was a homogeneous dispersion. The dispersion was coated out ona silicone release paper with a blade of approximately 20 milsthickness, to give a viscous coating on the surface of the releasecoating paper. After evaporation of the solvent, a film was obtainedwhich could be stripped readily from the release paper. This film had anelongation of over and the strength of the film was low. When wrapped onthe threads of a /2" bolt, and a nut applied, and torqued down to 30 ft.lbs. (416 k-g.-cm.), after 24 hours, an average of 55 ft. lbs. (762kg.-cm.) was required to break the nut away from the bolt. Washers couldalso be cut from the film and used as locking means.

Adhesive formulations were prepared using the capsules of Example I witha liquid polyarnide resin (V ersamid 125) as the curing agent. Theliquid polyamid capsule mixture was made solid and non-tacky by theaddition thereto of appropriate polymeric binders. The amounts ofcapsules, binder, and curing agent are listed in Table III. The valuesfor break-loose torque obtained by applying the adhesive formulation tothe underside of the heads of /2" bolts of the type described in ExampleI, tightening the bolts in place, and allowing the adhesive to cure, arealso given in Table III. Some of the bolts with the adhesive thereonwere aged at F. before being tightened into place. The values obtainedfor back-01f torque after this amount of aging are also given in Table11 III. Versamid 125 has over 200 atomic weight units per amine group.

agent being capable of undergoing storage at 120 F. under exposure tothe atmosphere for at least one week TABLE III Break-loose torque, ft.lbs, (kg-em.) Curing Sample Parts Capsules, agent, Aged, Number Binderbinder parts parts Initial 3-5 wks.

A 25% butadiene-styrene block copoly- 17 47.4 34.5 37 (514) 32 (444) merin toluene. B 25% low molecular weight hutadiene- 52.5 37.5 32 (444)(348) styrene block copolymer in toluene. C 10% GR-S typebutadiene-styrene 4 56 38 (528) 26 (361) eopolymer in toluene. D 10%polyvinyl butyral in toluene. 7.6 54 38.4 36 (500) 32 (444) E2OZ/b1isobutylene rubber (GR-I) in 5.9 54.9 38. 38 (528) 30 (416) 0none.

What is claimed is:

1. A stable locking cement composition which can be applied to thethreads of a bolt or other surface to be bonded to form a stable, solid,non-tacky coating which can be shipped and stored for months before useand which is pressure-activatable and self-curing at ambienttemperatures to give a firmly adherent bond, comprising microscopicallysmall capsules having infusible pressure rupturable aminoplast polymershells, containing therewithin a liquid polyepoxide resins and a roomtemperature solid low volatility amine curing agent for said polyepoxideresin in an amount sufficient to cure said resin, said amine curingagent being capable of undergoing storage at 120 F. under exposure tothe atmosphere for at least one week without loss of more than 2%thereof due to vaporization, said amine having at least about atomicweight units per amine group, said microcapsules and said curing agentbeing homogeneously dispersed within an organophilic non-hygroscopicfilm-forming organic polymeric binder, said binder being stablydispersible in solvents which are substantially free of highly polarfunctional groups and which have a solubility parameter of less thanabout nine, said composition containing less than about 1% water.

2. A composition according to claim 1 useful as a fastener sealantwherein said curing agent is an amine which will convert said epoxideresin to a hard infusible state within eighteen hours after rupture ofsaid capsules.

3. A composition according to claim 1 which is normally solid at roomtemperatures, in which said binder is thermoplastic whereby saidcomposition can be applied to a fastener in a molten condition atmoderately elevated temperatures.

4. A composition according to claim 1 wherein said binder, capsules andcuring agent are contained in the volatile non-polar organic solventcompatible with the capsules.

5. A composition according to claim 4 wherein said binder is polyvinylbutyral and said solvent is toluene.

6. A composition according to claim 1 in which said binder is a rubberypolymeric material, said composition being in the form of a thin film.

7. A composition according to claim 1 wherein said amine isl,3-di-4-piperidylpropane.

8. A composition according to claim 1 wherein said amine is imidazole.

9. A stable locking cement composition which can be applied to thethreads of a bolt or other surface to be bonded to form a stable, solid,non-tacky coating which can be shipped and stored for months before useand which is pressure-activatable and self-curing at ambienttemperatures to give a firmly adherent bond, comprising microscopicallysmall capsules having infusible pressure rupturable aminoplast polymershells, containing therewithin a liquid polyepoxide resin having morethan one 1,2-epoxy groups per molecule and about a stoichiometric amountof a room temperature solid low volatility amine curing agent for saidpolyepoxide resin, said amine curing without loss of more than 2%thereof due to vaporization, said amine having at least about 50 atomicweight units per amine group, said microcapsules and said curing agentbeing homogeneously dispersed within an organophilic non-hygroscopicfilm-forming organic polymeric binder selected from the group consistingof butadiene styrene copolymers, butadiene acrylonitrile copolymers,polyvinyl butyral, butyl rubber, polyamide resins and polyurethaneresins containing less than about 1% water.

10. A stable locking cement composition which can be applied to thethreads of a bolt or other surface to be bonded to form a stable, solid,non-tacky coating which can be shipped and stored for months before useand which is pressure-activatable and self-curing at ambienttemperatures to give a firmly adherent bond, comprising microscopicallysmall capsules having infusible pressure rupturable aminoplast polymershells, containing therewithin a liquid polyepoxide resin having morethan one 1,2-epoxy groups per molecule and a room temperature solid lowvolatility amine curing agent for said polyepoxide resin in an amountsufiicient to cure said polyepoxide resin, said amine curing agent bingcapable of undergoing storage at F. under exposure to the atmosphere forat least one week without loss of more than 2% thereof due tovaporization, said amine having at least about 50 atomic weight unitsper amine group, said microcapsules and said curing agent beinghomogeneously dispersed within an organophilic non-hygroscopic organicpolymeric binder selected from the group consisting of butadiene styrenecopolymers, butadiene acrylonitrile copolymers, polyvinyl butyral, butylrubber, polyamine resins and polyurethane resins containing less thanabout 1% water.

11. A stable locking cement composition which can be applied to thethreads of a bolt or other surface to be bolted to form a stable, solid,non-tacky coating, said coating being pressure-activatable andself-curing at ambient temperatures to give a firmly adherent bond,comprising: microscopically small capsules having infusible pressurerupturable aminoplast polymer shells, said polymer shells containingtherewith a liquid polyepoxide rein having more than one 1,2-epoxygroups per molecule; an amine curing agent comprising1,3-bis-4-piperidyl propane; and a polyvinyl butyral resin bindercontaining less than about 1% water; said microcapsules and said aminecuring agent being homogeneously dispersed within said polyvinyl butyralresin binder.

12. A stable locking cement composition which can be applied to thethreads of a bolt or other surface to be bonded to form a stable, solid,non-tacky coating which can be shipped and stored for months before useand which is pressure-activatable and self-curing at ambienttemperatures to give a firmly adherent bond, comprising microscopicallysmall capsules having infusible pressure rupturable aminoplast polymershells, containing therewithin a liquid polyepoxide resin and a roomtemperature solid low volatility amine salt curing agent for saidpolyepoxide resin in an amount sutficient to cure said resin,

said amine salt curing agent being capable of undergoing storage at 120F. under exposure to the atmosphere for at least one Week Without lossof more than 2% thereof due to vaporization, said amine salt being thesolid reaction product of a liquid amine and an acid, said microcapsulesand said amine salt curing agent being homogeneously dispersed within anorganophilic non-hygroscopic film-forming organic polymeric binder, saidbinder being stably dispersible in solvents which are substantially freeof highly polar functional groups and which have a solubility parameterof less than about nine, said composition containing less than about 1%water.

References Cited UNITED STATES PATENTS 3,173,878 3/1965 Reyes 117-36.8

14 4/1965 Schultz 161186 12/19 66 Dalton 252316 7/1968 Washburn 260-610/1968 Reyes 117-36.8 6/ 1970 Matson 11736.8 6/1970 Matson 117-400 C12/1966 Datton 8537 FOREIGN PATENTS 1966 Netherlands.

PAUL LIEBERMAN, Primary Examiner U.S. C1. X.R.

15 11736.8, 100 C; l517, 14.5; 26018 PN, 23 Ep, 28,

28.5 AS, 47 EN, 830 P, 836, 837 R, DIG. 33

Patent No UNITED STATES PATENT OFFICE Dated February 15, 1972Inventor(s) In Column 5,

In Column 8,

and

In Column 12,

(SEAL) Attest:

line line line line Column 11, line 27,

line line line line Signed and sealed EDWARD M.FLETCHER,JR. AttestingOfficer Fred w. Deckert and Gale w. Matson It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

In Column 1, line 2 of the Abstract, "therefore" should be therefor gand60, "commercial" should be commercially 25, "l. 6-hexane diamine" shouldbe 1,6-hexane diamine a 51, "furforyl" should be furfuryl 5 dete.32s.... h5rrP2fler resins" in Claim 1 should be resin 39, "hing"should be being g 48, "polyamine should be polyamide g 57, "rein" shouldbe resin and 58, "groups" should be group this 27th day of March 1973'.

ROBERT GOTTSCHALK Commissioner of Patents FORM PO-105O (10-59} USCOMM-DC6O376-P69 U.Sv GOVERNMENT PRINT NG OFFICE; 959 0-366-334

